1. Field of the Invention
The invention relates to a panel assembly comprising a number of rectangular flat panels interconnected mutually by hinges such that the assembly from a first state, in which the panels are folded upon each other into a package, can be brought into a second state in which the panels are situated alongside each other.
2. Description of the Related Art
Such panel assemblies whereby at least some panels carry solar cells are already known, e.g. from U.S. Pat. Nos. 5,487,791 and 5,509,747. In the first state the panels of these assemblies are folded zigzag wise into a package and in the second state the panels are unfolded and are oriented alongside each other in the same plane, forming one larger solar panel assembly.
Instead of solar cells any other suitable devices could be connected to the panels such as one or more cooling radiators, a number of mirrors, etc. In fact it is not even necessary that other components are attached to the panels. The panels as such can be used for instance for reflecting electromagnetic energy such as radio or radar waves.
Other known assemblies are described in U.S. Pat. No. 5,520,747 and EP 0754626. Wherein a central panel is adjoined by two side panels which in the first state both are folded just as window shutters on top of the same surface of the central panel and in the second state are unfolded and oriented along the central panel under a predetermined angle. In the unfolded state the mirrors, carried by the side panels will reflect sun light on the solar cells carried by the central panel.
In fact U.S. Pat. No. 5,520,747 describes a combined assembly whereby all central panels are unfolded zigzagwise whereafter the side panels connected to each central panel are unfolded window shutter wise.
Before transport the panels of such a panel assembly are folded into a package of which the length and width correspond approximately with the length and width of one separate panel and of which the thickness corresponds approximately with the thickness of one panel multiplied by the number of panels thereby greatly reducing the volume occupied by the assembly. In this state the assembly is transported from the earth into an orbit in space. In general the transporting vehicle (rocket, space shuttle, etc.) is able to transport payloads of rather restricted dimensions and restricted weight. Therefore, it is required in general that solar panel assemblies have a low weight and dimensions which should be within certain limits. To maintain a low weight one could use stiffness-efficient constructions having a sufficient strength, such as constructions comprising a lot of air and still having a sufficient stiffness and strongness, such as for instance honeycomb sandwich panels.
In general the only way to reduce the dimensions of a solar panel assembly in its first state is to reduce the thickness of the actual panels. In case honeycomb sandwich constructions are used the only reduction possibility is to reduce the dimensions of the core. The surface, i.e. the length and width of each panel, will be selected as large as possible to obtain a large useful area for locating solar cells.
A too great a reduction of the weight may lead to a construction having too little stiffness, both in a stowed configuration and in the fully deployed configuration. During operation, that may lead to harmful bending and torsion movements or oscillating movements of the individual panels or of the assembly as a whole in its extended second state. Such movements may occur for instance in the situation in which the position of the assembly in relation to the carrying satellite has to be corrected.
Structural stiffness can be given to an extended solar panel assembly of relatively thin rectangular panels by curving each panel in a direction parallel to the panel edges to which the hinges between the panels are not attached. Such an embodiment is described in an older European application 97204099.2 in the name of Fokker Space.
Among systems to link the kinematics of neighboring panels of the solar panel assembly during unfolding from an undeployed position to a deployed position are systems employing motors, powered reels comprising cables, pulleys or the like. Examples of systems to synchronize the angular rotation of all the panels of he solar panel assembly during unfolding are those presented by U.S. Pat. Nos. 5,487,791 and 5,509,747.
In the first mentioned U.S. Pat. No. 5,487,791 a system is described which comprises in fact two of the above-mentioned assemblies which in the unfolded second state are positioned in the same plane alongside each other. Each panel of the first assembly is connected through a pivot hinge to an adjacent panel of the second assembly. These pivot hinges extend along the central line of the respective panels such that both assemblies can be unfolded from the first into the second state simultaneously, whereby the unfolding operation of the first assembly takes place in counterphase in relation to the unfolding operation of the second assembly. Especially because of the presence of the pivot hinges it is impossible to get the panels in one plane and consequently curving of the panels to provide structural stiffness to the panel assembly as a whole cannot be used.
The assembly described in U.S. Pat. No. 5,509,747 comprises an articulation arrangement whereby all hinge axes are mutually coupled by means of gear wheels, wire wheels and a number of endless wires running across pairs of wire wheels such that an unfolding movement between for instance the first two panels in the assembly is transferred to all the other hinges which will move simultaneously in the same way and in the same direction. Miniaturization of the control mechanisms will undoubtedly lead to very high mechanical stresses in the various sprocket wheels or chain wheels.